This new Ted Talk just came out yesterday. It explores a correlation between religion and fertility globally. Take a look (~13 min):
I think Rosling is a little dismissive of religion, but his point is well taken: declining fertility rates are better understood as a function of income, education, medical technology, female employment, etc. than of religious variation. (You've just got to love the way Hans makes those infographics that travel over time, too!)
I think this also brings perspective to the current debate going on in the U.S. over compulsory employer contraceptive coverage (which I've blogged about before). The USCCB and, increasingly, conservative Evangelicals want to frame this as an affront to the religious liberty to "respect life" and protect the "traditional" family. Rosling's research suggests that family planning (i.e. access to affordable/free birth control) is the key to the respect for life on the global scale. (Of course, it's not rationally about such things.) Religion might not be significant on the global level, but it's certainly constraining on the individual level as a matter of political influence. Oh, yeah, and don't forget that most (58%) lay Catholics in the U.S. believe that employers should be required to provide their employees with health care plans that cover contraception; that's a larger proportion than among Americans overall (55%).